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# Questions tagged [wilcoxon-mann-whitney-test]

The Wilcoxon rank sum test, also known as Mann-Whitney U test, is a non-parametric rank test to assess whether one of two samples has larger values than the other.

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### Is the Wilcoxon two-sample test maximally powered to detect proportional odds alternatives?

We know from the literature that The Wilcoxon-Mann-Whitney two-sample rank sum test is optimal for detecting simple location shifts when comparing two continuous random variables that each have a ...
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### Power calculations for Wilcoxon test

I am running a Wilcoxon test to compare means between two groups (control and experiment) of unequal sample sizes. The distribution is right skewed and bound by zero for both groups. I would like to ...
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### What model contains Wilcoxon's rank sum test?

As Frank Harrel mentions in the answer to Logistic regression and Wilcoxon test, Wilcoxon's rank sum test (aka Mann-Whithey test) is contained in the proportional odds logistic regression, which would ...
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### Hypothesis testing with non-iid observations

I have a dataset with observations which violate the independent and identically distributed (iid) assumption. The dataset is composed by a number of post-click conversion events (purchases on a ...
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### Is Mann Whitney U the right statistical test for this analysis?

I am studying the spatial interactions between coral at a specific reef. I have the abundances of each coral species at each site we studied. I also have already run statistical tests and basically ...
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### How to do a stratified nonparametric test?

I'm trying to use the "coin" (conditional inference) package to perform a stratified nonparametric test for difference in distribution (for count data). I tried a stratified Mann-Whitney-Wilcoxon ...
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### Comparison of two means when they are means of means?

I have two vectors "$A$" and "$B$". Each vector contains multiple mean values derived from observations. The two vectors are subsets of a sample that has been categorized into five vectors. All ...
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### Minimum sample for non parametric test?

Exactly how many sample to be minimum size for non parametric test? Right now i have 3 data with really2 small sample size 1. 5 pairs for wilcoxon signed rank test (pretest and postest in 1 place) 2. ...
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### Reporting Mann Whitney test rejecting the null hypothesis, but samples have equal medians

I'm using the Mann Whitney test to verify if two population samples are equal. If the p-value is less than alpha (in this case, 0.05) I reject the null hypothesis and use the median of each population ...
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### Comparing ROC-curves

I would like to find if there is a significant difference between two ROC-curves. I've found the roc.test in the pROC package. However, I cannot seem to find any information on how this test is ...
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### Multiple comparisons between two groups (non-parametric)

Update Added more details about the Experimental setup. My experiment comprised two groups, control (N=25) and experimental (N=26). Each participant belonged to one group. Their performance has been ...
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### Algebraic Manipulations in Mann-Whitney-Wilcoxon Test Statistics

Given Let $\Delta > 0$ be positive real number. Consider the Wilcoxon-Mann-Whitney upper tail test $H_0: \Delta \leq 0 \,\,\, \text{vs} \,\,\, H_a: \Delta > 0$ aimed at testing the difference ...
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### Statistical method comparing difference in extreme percentile

Statistical methods like wilcox.test to t.test test differences in medians or means. I would like to compare the difference in ...
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### Can non-parametric tests, e.g. Mann-Whitney U, be used on non-normally distributed statistics off of bootstrap samples?

I have some return data from some different portfolios which I would like to compare using risk vs return ratios. The standard Sharpe ratio has a nice solution for calculating the significance of the ...
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### Combining paired and unpaired samples in Wilcoxon/MWU test

I am trying to compare numbers in two sets (X and Y) to test if numbers in one of the set are statistically larger than the others. However, some of the numbers are paired, and some are not. For ...
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### Wilcoxon Rank-Sum vs Signed Rank for paired

I'm working with a dataset that contains paired samples (but some samples are missing their pair) and I want to check for an association between a binary variable and a bunch of numeric variables. ...
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### Manually computed Mann–Whitney U-test differs from R's output

I found a sketchy lecture notes about Mann–Whitney U-test. There where were given data X: 30 32 33 33 36 37 40 44 Y: 27 29 31 34 34 35 41 It was computed that ...
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### List of sample arrangements at a given Wilcoxon / Mann-Whitney test statistic

Consider a Wilcoxon-Mann-Whitney test statistic, either in the form (i) "W = sum of ranks in sample A"; or in the form (ii) "sum of ranks in sample A - the minimum possible sum of ranks in sample ...
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### Different ways to calculate the test statistic for the Wilcoxon rank sum test

There are different ways to calculate the test statistic for the Wilcoxon rank sum test (quote from R help): The literature is not unanimous about the definitions of the Wilcoxon rank sum and ...
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### Semi-parametric approach: nonparametric test of residuals from linear mixed model

I want to know if this is a reasonable approach. I conducted the same experiment on two different species with small sample sizes (7-25 per species) in 4 years at 6 different sites. I measured damage ...
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### Why does one get a 0.000 Mann-Whitney U value (not p-value) etc.?

1) Is it okay to run a Mann-Whitney U test on unequal sample sizes i.e. two groups (N=11, N=12)or is there an alternative test? 2) What does it mean when one obtains a zero value for a Mann-Whitney U ...
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### Most appropriate test for count data

So I've performed an experiment whereby I had 12 1km transects. 6 of these were along rivers running through agricultural land and 6 through woodland. These were arranged in pairs so that each agri ...
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### How to bootstrap for the standard error of a two sample test

I want to calculate the standard error of the area under the curve computed with the Mann-Whitney U-Test (MWUT). Hanley and McNeil 1982 give a formula for it (they call the AUC calculated with the ...
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### Unbiasedness Wilcoxon-Mann-Whitney Test

There are many different alternatives discussed for the Wilcoxon-Mann-Whitney test. One alternative is $P(X < Y) + \frac{1}{2}P(X = Y) \neq 0.5$. There are compelling arguments for this, such as ...
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### rank-sum test vs. anova

I have a set of data looks like this: hwid freq code output 101 5150 764 24 101 5170 768 24 101 5190 764 24 102 5150 752 24 102 5170 760 24 ... ... ... 24 The data represents "power level&...
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### How to know if I have enough sample for a small sample t-test to be appropriate?

Say I have 15 or 20 samples each from two samples. The data shows evidence of strong skew. I am considering a two-sample t-test of means, based on the assumption that the sampling distribution of the ...
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### When to use Spearman correlation and when to use Wilcoxon Rank sum test?

I have collected data on 1680 test scores and 1680 participation rates from 7 different courses and 4 different semesters using information from 60 students. I am confused of whether to use a ...
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### Fisher exact test for enrichment of subpopulations in single cell data

We have single cell data from 12 control and 12 diseased individuals. The data has been integrated (remove batch effects) and clustered. We would like to know if there are any clusters that are ...
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### How to conduct a boostrapped or a permutation wilcoxon test (in R)

I have a total of 18 mice, 9 from Healthy group and 9 from Sick group. Since I have a very poor sample size I would like to use boostrapping or permutation test. Is there a way to conduct a ...
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### Mann-Whitney U Test test valid for percentages (% seagrass cover)?

Is the Mann-Whitney U Test test valid for percentages (not counts, but percent cover of seagrass)? All my data points are average percent cover of seagrass with about 53% of the data being zeros ...
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### How can I explain signifcant combined groups in Mann Whitney U but no individual effects in Kruskal Wallis?

I am struggling to get my head around the concepts of my tests and how to explain them. Unfortunately we didn't recieve much in depth teaching about it on my course. I have 4 variables, one is a ...
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### How do I determine whether there is a significant difference between two sets of price data?

I am conducting a study where I am collecting prices from two groups of funeral homes in a particular state: in the first group, the homes I collected prices from are owned by families, and in the ...
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### Actual difference between the statistic results from scipy.stats.ranksums and scipy.stats.mannwhitneyu

So, I have been trying to test if two independent samples come from the distribution, i.e. if they are greater or less than one another. Eventually I found out the Mann Whitney U Test is the ...
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### Testing tuples of response variables

I'm struggling with comparing samples with multiple response variables, where such variables have a strict precedence or importance order. For the sake of this exercise, let's assume that each sample ...
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### Estimating distribution of tied ranks for tie correction to Wilcoxon-Mann-Whitney U test

Tests based on ranking elements, such as Mann, H. B.; Whitney, D. R. On a Test of Whether one of Two Random Variables is Stochastically Larger than the Other. Ann. Math. Statist. 18(1):50-60, 1947, ...
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### Non-parametric test for station variation

Certain disease reduces the concentration of calcium in people's blood. To test the effectiveness of a drug for the treatment of the disease, 9 individuals with the disease underwent an assessment in ...
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### One-sample versions of the signed rank and rank sum tests?

I wonder if there are applications of the signed rank and rank sum tests in a one-sample context? Signed rank Is there a form of the signed rank test where the difference $A-B$ for each subject is ...
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### Test for different median in two independent groups with repeated measurements

I want to test if the median of a continuous variable (e.g. height) is the same in two independent groups (boys and girls). For each person there are multiple measurements of the continuous variable ...
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### If Mann-Whitney U is a median test? Then what the heck is "unpaired pairwise median"?

Header: I am really sorry for the confusing title. I am going to edit it so it fits the responses I get based on Mann Whitney U. So I had this exact question on stack overflow about is the Mann ...
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### Testing differences in 5 star rating (Which hotel to choose)

Say, I want to choose a Hotel with the following ratings (1-5) on TripAdvisor. This seemed interesting if the mean for the Hotel with smaller number of votes is bigger than the mean of the hotel with ...
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### Go with t-test or Mann-Whitney U test?

I'm measuring performance of 2 methods (method_A and method_B) that try to satisfy customers demands. Both methods produce ...
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### Whitney-Mann and multiple regression

Is it appropriate to use Whitney-Mann (to compare the groups) and multiple Regression model (to analyse each factor) within the same data? (parametric and non-parametric test on the same data)
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### Wilcoxon Test with Random Effect

I would like to test if there is a significant difference in the speed of movement between 2 treatments for different females. For each female, I have several sampling points. I have a table with the ...
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### multi-level Wilcoxon analysis

The question was originated from the paper [1] Table 3 [2], for every species, there was a data frame with two column: disease categories and the conservation index. Conservation index is numeric. The ...
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### Sample size for multiple hypothesis test: Wilcoxon test and Benjamini–Hochberg procedure

I have an experiment with a control and multiple treatments and want to find which one performs the best. I would use the Wilcoxon pairwise test to test all the hypotheses and correct the p-values ...
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### Adjusting P-Values of one-tailed tests

I am running a large number of two-sample Wilcox tests and using Benjamini, Hochberg, and Yekutieli method to adjust the p-values. The issue is that when I conduct a one-tailed test, the p-values ...
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### T- tests on non-normal data

I keep reading mixed things about doing t-tests on non-normal data when the sample sizes are large and I don't know what to believe. I have large samples sizes, over 1000 but the distribution is by ...
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### Groups with very unequal sizes

I want to compare means of the data of two human populations, group A has 12,400 (91.7%) subjects and group B has 1118 (8.3%). These are further subdivided to groups A1 (7598, 93.8%), B1 (499, 6.4%), ...
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### Mann Whitney U test or Kruskall-Wallis + Dunn test as a post hoc?

I performed a set of inhibition experiments where Lactobacilli supernatants where tested against a pathogen cell culture. These experiments were carried out in a 96-well plate where pathogen was ...
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